Converter: Replace deprecated string_concat

Change the use of string_concat with format_lazy.
string_concat is deprecated in Django 1.11 and removed in
Django 2.1.

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

mayan/apps/converter/transformations.py

@@ -5,7 +5,8 @@ import logging
 
 from PIL import Image, ImageColor, ImageFilter
 
-from django.utils.translation import string_concat, ugettext_lazy as _
+from django.utils.text import format_lazy
+from django.utils.translation import ugettext_lazy as _
 from django.utils.encoding import force_bytes
 
 logger = logging.getLogger(__name__)
@@ -51,7 +52,9 @@ class BaseTransformation(object):
     @classmethod
     def get_label(cls):
         if cls.arguments:
-            return string_concat(cls.label, ': ', ', '.join(cls.arguments))
+            return format_lazy(
+                '{}{}{}', cls.label, ': ', ', '.join(cls.arguments)
+            )
         else:
             return cls.label
 

mayan/apps/metadata/forms.py

@@ -3,7 +3,8 @@ from __future__ import unicode_literals
 from django import forms
 from django.core.exceptions import ValidationError
 from django.forms.formsets import formset_factory
-from django.utils.translation import string_concat, ugettext_lazy as _
+from django.utils.text import format_lazy
+from django.utils.translation import ugettext_lazy as _
 
 from .classes import MetadataLookup
 from .models import DocumentTypeMetadataType, MetadataType
@@ -146,8 +147,8 @@ class DocumentAddMetadataForm(forms.Form):
 class MetadataTypeForm(forms.ModelForm):
     def __init__(self, *args, **kwargs):
         super(MetadataTypeForm, self).__init__(*args, **kwargs)
-        self.fields['lookup'].help_text = string_concat(
-            self.fields['lookup'].help_text,
+        self.fields['lookup'].help_text = format_lazy(
+            '{}{}{}', self.fields['lookup'].help_text,
             _(' Available template context variables: '),
             MetadataLookup.get_as_help_text()
         )